Generate source map files with long extentions (e.g. .js.map)

[kirillrogovoy]

↪️ Pull Request

Closes #2460.

What I do here is preserve the original file extension before appending .map to the source map files.

Instead of index.map it would generate index.js.map. According to the spec it's the recommended convention. It also solves a real issue for debugging Javascript in VSCode.

While it solves the issue, I don't like the tech debt I introduce. Specifically, I don't like the conditionals about specific types of bundles in the otherwise abstract code.

@DeMoorJasper please, take a look and let me know if you can think of a more pleasing solution architecture-wise. This is my first peek at the internals of Parcel, so I don't have the whole context yet.

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs

[DeMoorJasper]

I think there was no nice way of solving this. It works and it's not that bad, so I guess it's good enough